Balanced multi-cavity injection molding of like plastic products

ABSTRACT

Balanced injection molding in a multi-cavity mold of a plurality of ridged-wall products having is accomplished by providing mold parts defining therebetween at least two cavities for forming the ridged-wall plastic products, wherein each of at least two cavities defines a plurality of flow channels in which injected plastic material flows within the cavity and in which flow channels the first side strips are formed; wherein the relative disposition of the mold parts is adjustable for adjusting the dimensions of the flow channels in at least two mold cavities separately so that when plastic material is injected approximately simultaneously into the at least two mold cavities the injected plastic material flows within the at least two cavities at respective flow rates that cause the at least two mold cavities to be completely filled approximately simultaneously with the injected plastic material.

This is a continuation of application Ser. No. 08/585,272 filed Jan. 10,1996, now U.S. Pat. No. 5,858,286.

BACKGROUND OF THE INVENTION

The present invention generally pertains to injection molding of plasticproducts and is particularly directed to balanced multi-cavity injectionmolding of plurality of like products.

One type of product for which it is a difficult to provide balancedfilling of the mold cavities when injection molding a plurality of likeproducts with a multi-cavity mold is a ridged-wall product including aplurality of longitudinal folds of alternating ridges and furrows, witheach fold including a first side strip laterally extending from the topof a said ridge to the bottom of a said furrow, and a second side striplaterally extending from the bottom of the said furrow to the top of asaid ridge next to the said ridge; wherein the first side strip has adifferent lateral orientation than the second side strip; and whereinthe first side strip has a greater wall thickness than the second sidestrip. Such a product is described in U.S. Pat. No. 5,267,685 to JensOle Sorensen.

For efficient manufacture, it is preferred to injection mold suchproducts simultaneously with a multi-cavity mold. A problem incident tomulti-cavity injection molding of such products is that all of thecavities of the mold in which the products are formed are not alwayscompletely filled simultaneously with the injected plastic material.Referring to FIG. 1, which illustrates a plurality of injection moldedhollow ridged-wall plastic products 10, 10a, 10b remaining in one moldpart 12 after the mold parts 12, 14 defining the respective cavities inwhich the products are formed have been separated, it is seen thatfailure to completely fill all of the mold cavities simultaneouslyresults in some of the cavities being incompletely filled, such that aproduct 10a therein is not completely formed, and other cavities beingoverfilled, such that a flashing of excess plastic 16 is attached to aproduct 10b formed therein. The gates through which the plastic materialis injected into the mold cavities are located at the center of the endof the respective cavities at which closed ends 18 of the hollow plasticproducts 10, 10a, 10b are formed.

SUMMARY OF THE INVENTION

The present invention provides a method of balanced injection molding ofa plurality of like plastic products in a multi-cavity mold, whereineach of at least two mold cavities defines a said like product, themethod comprising the steps of:

(a) providing mold parts defining therebetween said at least twocavities for forming said like plastic products; and

(b) injecting plastic material approximately simultaneously into said atleast two mold cavities to form the products;

wherein step (a) comprises the step of:

(c) prior to step (b), adjusting the relative dimensions of said atleast two mold cavities to be non-uniform such that when plasticmaterial is injected in accordance with step (b) injected plasticmaterial flows within said at least two mold cavities at respective flowrates that cause said at least two mold cavities to be completely filledapproximately simultaneously with the injected plastic material.

Additional features of the present invention are described withreference to the detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a mold utilized in a prior artmulti-cavity injection molding method wherein a plurality of ridged-wallplastic products remain in one mold part after the mold parts definingthe product-forming cavities have been separated.

FIG. 2 is a side sectional view of a preferred embodiment of a mold forforming ridged-wall products in accordance with the present invention.

FIG. 3 top view of a first mold part of the mold of FIG. 2, withadjustment blocks disposed in portions of the first mold part.

FIG. 4 is a sectional view of a portion of the mold of FIG. 2 takenalong line 4--4 when the first and second mold have a given dispositionin relation to one another.

FIG. 5 is a sectional view corresponding to FIG. 4 wherein the secondmold part has a different disposition in relation to the first mold partthan that shown in FIG. 4.

FIG. 6 is another sectional view corresponding to FIG. 4 wherein thesecond mold part has a different disposition in relation to the firstmold part than that shown in FIGS. 4 and 5.

FIG. 7 is a sectional view of the mold of FIG. 2 taken along line 7--7when the first and second mold parts have a relative disposition asshown in FIG. 4.

FIG. 7A is an enlarged view of a portion of the mold cavity definedbetween first and second mold parts having the relative dispositionshown in FIG. 7. Said portion is encircled in FIG. 7.

FIG. 8 is a sectional view of the mold of FIG. 2 taken along line 7--7when the first and second mold parts have a relative disposition asshown in FIG. 5.

FIG. 8A is an enlarged view of a portion of the mold cavity definedbetween first and second mold parts having the relative dispositionshown in FIG. 8. Said portion is encircled in FIG. 8.

FIG. 9 is a sectional view of the mold of FIG. 2 taken along line 7--7when the first and second mold parts have a relative disposition asshown in FIG. 6.

FIG. 9A is an enlarged view of a portion of the mold cavity definedbetween first and second mold parts having the relative dispositionshown in FIG. 9. Said portion is encircled in FIG. 9.

DETAILED DESCRIPTION

Referring to FIGS. 2 through 9A, a preferred embodiment of the mold ofthe present invention includes a first mold part 20 and a second moldpart including at least two segments 22 which when combined with thefirst mold part 20 define therebetween at least two cavities 24 forrespectively forming ridged-wall plastic products, such as described inthe above-referenced U.S. Pat. No. 5,267,685. Each product includes aplurality of longitudinal folds of alternating ridges and furrows. Eachfold includes a first side strip laterally extending from the top of oneridge to the bottom of one furrow; and a second side strip laterallyextending from the bottom of the one furrow to the top of another ridgenext to the one ridge. The first side strip has a different lateralorientation than the second side strip and the first side strip has agreater wall thickness than the second side strip. Each mold cavity 24defines a plurality of flow channels 26 in which injected plasticmaterial flows within the cavity 24. The first side strips are formed inthe flow channels 26.

The respective disposition of the at least two separate segments 22 ofthe second mold part in relation to the first mold part 20 areseparately adjustable for adjusting the dimensions of the flow channels26 in the at least two mold cavities 24 separately so that when plasticmaterial is injected approximately simultaneously into the at least twomold cavities 24 the injected plastic material flows within the at leasttwo cavities 24 at respective flow rates that cause the at least twomold cavities 24 to be completely filled approximately simultaneouslywith the injected plastic material.

When the product is a hollow product, the separate segments 22 of thesecond mold part are separately rotatable in relation to the first moldpart 20 for adjusting the dimensions of the flow channels 26 of therespective cavities 24.

When the first mold part 20 is joined at a parting line P.L. to theseparate segments 22 of the second mold part to define the respectivecavities 24 therebetween, a plurality of adjustment spaces 28 are alsodefined about the parting line P.L. between portions of the first moldpart 20 and portions of the respective segments 22 of the second moldpart.

Bolts 30 that are anchored to the first mold part 20 extend into each ofthe adjustment spaces. Adjustment blocks 32 are screwed onto the bolts30 for disposition in the adjustment spaces 28 in order to lock therespective segments 22 of the second mold part in a fixed position inrelation to the first mold part 20 when the first mold part 20 and therespective segments 22 of the second mold part are joined at the partingline P.L. The blocks 32 each have a first section 34 for disposition inat least a region of the adjustment space 28 on the same side of theparting line P.L. as the first mold part 20 and a second section 36 fordisposition in at least a region of the adjustment space 28 on the sameside of the parting line as the segment 22 of the second mold part.There are a plurality of sets of blocks 32 for enabling differentdegrees of adjustment between the first mold part 20 and the respectivesegments 22 of the second mold part; and the disposition of the firstsection 34 in relation to the second section 36 is different for thedifferent sets of blocks 32. With reference to the disposition of asegment 22 of the second mold part in relation to the first mold part20, as shown in FIG. 7, that is provided when the relative dispositionbetween the first section 34 and the second section 36 of the block 32is as shown in FIG. 7A, a set of blocks 32 having the relativedisposition between the first section 34 and the second section 36 ofthe block 32 shown in FIG. 8A is used for rotating a segment 22 of asecond mold part counterclockwise in relation to the first mold part 20to provide the disposition of the segment 22 of the second mold part inrelation to the first mold part 20 that is shown in FIG. 8; and a set ofblocks 32 having the relative disposition between the first section 34and the second section 36 of the block 32 shown in FIG. 9A is used forrotating a segment 22 of a second mold part clockwise in relation to thefirst mold part 20 to provide the disposition of the segment 22 of thesecond mold part in relation to the first mold part 20 that is shown inFIG. 9.

In balancing the mold, the dimensions of the flow channels 26 initiallyare larger than required for forming first side strips of a preferreddimension, as shown in FIG. 9A; and plastic material is injected at agiven injection pressure approximately simultaneously into the at leasttwo mold cavities 24 in order to form the products with the injectedplastic material. The relative extent to which the different cavities 24are filled with the injected plastic material is measured. When the atleast two mold cavities 24 are not filled to the same degreeapproximately simultaneously, the relative dimensions of the flowchannels 26 are adjusted so that when plastic material is injected intothe mold cavities 24, the injected plastic material flows within the atleast two cavities at respective flow rates that cause the at least twomold cavities 24 to be filled to the same degree approximatelysimultaneously with the injected plastic material.

The relative dispositions between a segments 22 of the second mold partand the second mold part 20 are adjusted by inserting respective sets ofblocks 32 into the adjustment spaces 28.

Preferably, the dimensions of the flow channels 26 of the respectivecavities 24 are adjusted such that the flow channels 26 for at least oneof the mold cavities 24 are of a dimension required for forming firstside strips of the preferred dimension, as shown in FIG. 7A. Sometimes,the flow channels 26 for at least another of the mold cavities 24 areeither of a dimension larger than required for forming first side stripsof the preferred dimension, as shown in FIG. 9A, or of a dimensionsmaller than required for forming first side strips of the preferreddimension, as shown in FIG. 8A. The relative differences between thedimensions of the flow channels shown in FIGS. 7A, 8A and 9A are greatlyexaggerated in the Drawing.

However, if such an adjustment does not result in the injected plasticmaterial flowing within the at least two cavities 24 at respective flowrates that cause the at least two mold cavities 24 to be filled to thesame degree approximately simultaneously with the injected plasticmaterial, the dimensions of the flow channels 26 of the respectivecavities 24 are adjusted such that the flow channels 26 for at least oneof the mold cavities 24 are of a dimension larger than required forforming first side strips of the preferred dimension, as shown in FIG.9A, and the flow channels 26 for at least another of the mold cavities24 are of a dimension smaller than required for forming first sidestrips of the preferred dimension, as shown in FIG. 8A.

When such adjustments result in the injected plastic material flowingwithin the at least two cavities 24 at respective flow rates that causethe at least two mold cavities 24 to be filled to the same degreeapproximately simultaneously with the injected plastic material, themulti-cavity mold is provided for balancing injection molding of aplurality of ridged-wall products and plastic material is injectedapproximately simultaneously into the at least two mold cavities 24 toform such products.

In alternative embodiments (not shown), either or both of the first moldpart and the second mold part includes segments of which the dispositionmay be adjusted in relation to the other mold part in order to cause theinjected plastic material to flow within the at least two cavities atrespective flow rates that cause the at least two mold cavities to befilled to the same degree approximately simultaneously with the injectedplastic material.

The advantages specifically stated herein do not necessarily apply toevery conceivable embodiment of the present invention. Further, suchstated advantages of the present invention are only examples and shouldnot be construed as the only advantages of the present invention.

While the above description contains many specificities, these shouldnot be construed as limitations on the scope of the present invention,but rather as exemplifications of the preferred embodiments describedherein. Other variations are possible and the scope of the presentinvention should be determined not by the embodiments described hereinbut rather by the claims and their legal equivalents.

We claim:
 1. A method of balanced injection molding of a plurality oflike plastic products in a multi-cavity mold, wherein each of at leasttwo mold cavities defines a said like product, the method comprising thesteps of:(a) providing mold parts defining therebetween said at leasttwo cavities for forming said like plastic products; and (b) injectingplastic material approximately simultaneously into said at least twomold cavities to form the products;wherein step (a) comprises the stepof: (c) prior to step (b), adjusting the relative dimensions of said atleast two mold cavities to be non-uniform such that when plasticmaterial is injected in accordance with step (b) injected plasticmaterial flows within said at least two mold cavities at respective flowrates that cause said at least two mold cavities to be completely filledapproximately simultaneously with the injected plastic material.
 2. Amethod according to claim 1; wherein each of said at least two cavitiesdefines a plurality of flow channels in which injected plastic materialflows within the cavity, andwherein the relative dimensions of the flowchannels in said at least two mold cavities defined by the mold partsprovided in accordance with step (a) are non-uniform.
 3. A method ofbalanced injection molding of a plurality of like plastic products in amulti-cavity mold, wherein each of at least two mold cavities defines asaid like product, the method comprising the steps of:(a) providing moldparts defining therebetween said at least two cavities for forming saidlike plastic products; and (b) injecting plastic material approximatelysimultaneously into said at least two mold cavities to form theproducts;wherein step (a) comprises the step of: (c) adjusting therelative dimensions of said at least two mold cavities to be non-uniformsuch that when plastic material is injected in accordance with step (b)injected plastic material flows within said at least two mold cavitiesat respective flow rates that cause said at least two mold cavities tobe completely filled approximately simultaneously with the injectedplastic material; wherein said like products are ridged-wall products,each comprising a plurality of longitudinal folds of alternating ridgesand furrows, each fold including a first side strip laterally extendingfrom the top of a said ridge to the bottom of a said furrow; and asecond side strip laterally extending from the bottom of the said furrowto the top of a said ridge next to the said ridge; wherein the firstside strip has a different lateral orientation than the second sidestrip; and wherein the first side strip has a greater wall thicknessthan the second side strip; wherein each of said at least two cavitiesdefines a plurality of flow channels in which injected plastic materialflows within the cavity and in which flow channels the first side stripsare formed; and wherein the relative dimensions of the flow channels insaid at least two mold cavities defined by the mold parts provided inaccordance with step (a) are non-uniform.